This invention relates generally to a slant-type drilling rig assembly for drilling boreholes having an inclined axis. More specifically, this invention relates to apparatus for transferring conduit sections between an inclined drilling mast and a structure for storing conduit sections in a generally vertical posture.
In the past, it has been known to use drilling rig assemblies in which an inclinable drilling mast may be positioned to obtain inclined boreholes and to permit a plurality of boreholes to be drilled from a single location. The desirability of having a plurality of boreholes is more readily visualized in the context of widely used off-shore drilling platforms.
Where inclined drilling masts are used, previously known conventional racking assemblies for conduit storage have proved to be unsatisfactory for a variety of reasons. Among the reasons is the fact that the inclined masts are preferably designed to operate in a plurality of positions with different angular relationship to a vertical direction. Accordingly, numerous alternate structures have been proposed to alleviate at least some of the disadvantages of theretofore known racking assemblies.
With the introduction of racking structures spaced from the drilling mast, there arose a need for suitable apparatus to transfer conduit sections composed of one or more joints of drill pipe back and forth between the racking structure and the drilling mast. In some of the known types of transfer apparatus, a shuttle, carriage, or the like has been used to transport a conduit section between an inclined mast and a vertical pipe storage area. Typically, these shuttle systems require cable systems of varying degrees of complexity to control movement of the shuttle between the mast and the storage area.
In addition, the shuttle systems generally require two workmen: one workman atop the storage area to position conduit sections therein and to connect conduit sections to the shuttle; one workman in the drilling mast to connect conduit sections with the shuttle and to connect conduit sections to a travelling block of the mast. It should be apparent that elimination of one workman would be advantageous both in the sense of dollar economy and of efficient personnel use.
Since some of the shuttle systems recognize the need for operating between various inclined positions, they have been provided with generally arcuate tracks on which the shuttle moves. Such curved tracks, however, are expensive to manufacture. Accordingly, some systems have suggested the use of straight tracks for the shuttle. However, straight tracks do not compensate for the vertically lower position which corresponding points of an inclined mast assume with respect to the storage area by virtue of the arcuate movement of the mast to the inclined position. Therefore, the straight track systems introduce additional complexity into their apparatus to accommodate for the vertical displacement of corresponding points.
Other known types of systems have employed catwalk structures of various designs which extend between the storage area and the inclined drilling mast. In use, a workman may physically push or guide the upper end of a conduit section during its transfer between the mast and storage. These catwalks may thus quickly lead to physical fatigue of the workman.
Another objectionable feature of the known transfer devices is that a catline is frequently used to move the lower end of the conduit from the mast to the storage area. Such catlines present danger to workmen on the deck of the drilling rig in addition to making the conduit transfer procedure more complex.
When dealing with horizontal conduit storage areas, pivotally mounted frames have also been used in the past to raise and lower conduit sections to mast structures for connection with other conduit sections. Such known pivotally mounted frames typically require two workmen: one in the storage area and one on the mast. Moreover, relatively large surface areas are required for pipe storage and for movement of the pivotally mounted frame.